Introduction to the Plant Kingdom: Bryophytes

1. Introduction to the Plant Kingdom: Bryophytes Chapter 20

2. Outline • Introduction • Introduction to the Bryophytes • Phylum Hepaticophyta – Liverworts • Phylum Anthocerophyta – Hornworts • Phylum Bryophyta – Mosses • Human and Ecological Relevance of Bryophytes

3. Introduction • Plants and green algae share: • Chlorophylls a and b, carotenoids • Starch as food reserve • Cellulose in cell walls • Phragmoplast and cell plate during cell division • Shared features suggest common ancestor • Land plants first appeared 400 mya • Ancestor progressed from aquatic to land habitat even earlier

4. Introduction • Features preventing dessication: • Plant surfaces developed fatty cuticle to retard H2O loss • Gametangia (gamete-producing structures) and sporangia (spore-producing structures) became multicellular and surrounded by jacket of sterile cells • Zygotes developed into multicellular embryos within parental tissues originally surrounding egg

5. Introduction to the Bryophytes • Ca. 23,000 species of bryophytes • Include mosses, liverworts, and hornworts • Occupy wide range of habitats: • Damp banks, trees, logs • Bare rocks in scorching sun • Frozen alpine slopes • In elevations from sea level up to 5,500 m or more

6. Introduction to the Bryophytes • Bryophytes often have mycorrhizal fungi associated with rhizoids • Peat mosses ecologically important in bogs • Luminous mosses found in caves and other dark, damp places • None have true xylem or phloem • Many have hydroids for H2O conduction • Most H2Oabsorbed directly through surface • Few have leptoids for food-conduction • Need H2O to reproduce sexually

7. Introduction to the Bryophytes • Exhibit alteration of generations • In mosses, leafy plant = gametophyte generation • Sporophyte generation grows from gametophyte • 3distinct bryophyte phyla • None appear closely related to other living plants • Bryophyte lines may have arisen independently from ancestral green algae

8. Phylum Hepaticophyta – Liverworts • Structure and form: • Most common and widespread liverworts have flattened, lobed thalli (singular: thallus) • Thalloid liverworts constitute ca. 20% of spp. • Other 80% leafy • Thalli or leafy gametophytes develops from spores • When spores germinate they may produce protonema - immature gametophyte consisting of short filaments • Thalloidliverworts growth prostrate and one-celled rhizoids on lower surface anchor plant

9. Phylum Hepaticophyta – Liverworts • Thalloid liverworts • Best known species in genusMarchantia • Thallus forks dichotomously as it grows • Each branch apical notch and central groove • Meristematic cells in notch continue to divide • Bottom layer of thallus - epidermis from which rhizoids and scales arise

10. Phylum Hepaticophyta – Liverworts • Marchantia • Upper surface divided into diamond-shaped segments marking limits of chambers below • Each segment has small bordered pore opening into chamber • Short, erect rows of cells with chloroplasts sit on floor of chambers

11. Phylum Hepaticophyta – Liverworts • Thalloid liverworts • Marchantia- asexual reproduction: • Gemmae(singular: gemma) - tiny, lens-shaped pieces of tissue become detached from thallus • Produced in gemmae cupsscattered over upper surface of thallus

12. Phylum Hepaticophyta – Liverworts • Thalloid liverworts • Marchantia- sexual reproduction: • Gametangia formed on gametophores • Male gametophore = antheridiophore • Antheridia containing flagellated sperm found on upper surface

13. Phylum Hepaticophyta – Liverworts • Marchantia- sexual reproduction cont’d.: • Female gametophore = archegoniophore • Archegonia with eggs in rows and hang down beneath spokes of archegoniophore

14. Phylum Hepaticophyta – Liverworts • Marchantia- sexual reproduction cont’d.: • Embryo dependent on gametophyte for sustenance • Foot of sporophyte anchors to archegoniophore • Seta - short stalk • Capsule - meiosis produces 1nsporesinside • Also contains 2nelaterswith spiral thickenings • Immature sporophyte protected by calyptra = caplike tissue that grows out from gametophyte

15. Phylum Hepaticophyta – Liverworts • Marchantia- sexual reproduction cont’d.:

16. Phylum Hepaticophyta – Liverworts • Leafy liverworts • 2 rows of partially overlapping leaves • No midrib • Often have folds or lobes • Cells contain oil bodies • 3rd row of underleaves often present • Archegonia and antheridia produced in cuplike structures composed of modified leaves, in axils of leaves or on separate branches • Sporophyte pushes out from among leaves

17. Phylum Anthocerophyta – Hornworts • Structure and form: • Mature sporophytes look like miniature greenish-blackish rods • Gametophytes thalloid • Cells with only 1 large chloroplast • Thalli have pores and cavities filled with mucilage often containing N2-fixing bacteria • Ca. 100 spp. worldwide • Asexual reproduction by fragmentation of thallus

18. Phylum Anthocerophyta – Hornworts • Sexual reproduction: • Archegonia and antheridia produced in rows just beneath upper surfaces of gametophytes • Sporophyte: • Numerous stomata • Meristem above foot continually increases length of sporophyte from base • Meiosis produces 1n spores • 2nelaters also produced

19. Phylum Bryophyta – Mosses • Structure, form and classes: • Ca. 15,000 spp. of mosses • Divided into 3 classes: • Peat mosses • True mosses • Rock mosses A true moss

20. Phylum Bryophyta – Mosses • Structure, form and classes cont’d.: • Leaves of moss gametophytes have blades nearly always one-cell thick, except at midrib, and never lobed or divided • Cells usually contain numerous chloroplasts • Peat moss leaves have large transparent cells without chloroplasts that absorb H2O; and small, green, photosynthetic cells sandwiched between • Axis stemlike, without xylem or phloem • Often with hydroids Cells of peat moss leaves

21. Phylum Bryophyta – Mosses • Sexual reproduction: • Gametangia at apices of leafy shoots • Archegonium cylindrical with egg in swollen base, and neck above containing narrow canal • Multicellular filaments = paraphyses scattered among archegonia

22. Phylum Bryophyta – Mosses • Sexual reproduction cont’d.: • Antheridia on short stalks, surrounded by walls 1 cell thick • Sperm cells, each with pair of flagella, formed inside • Sperm forced out top of antheridium • Paraphyses scattered among antheridia

23. Phylum Bryophyta – Mosses • Sexual reproduction cont’d.: • Archegonia release substances attracting sperm • Sperm swim down neck of archegonium • Zygote grows into spindle-shaped embryo • Top of archegonium splits off and forms cap on top of sporophyte = calyptra • Mature sporophyte consists of capsule, seta and foot

24. Phylum Bryophyta – Mosses • Sexual reproduction cont’d.: • Meiosis produces spores inside capsule • Peristome, composed of 1 or 2 rows of teeth, under operculum at tip of capsule • Peristome opens or closes in response to humidity • Spores develop into filamentous protonema that produces buds developing into leafy gametophytes

25. Phylum Bryophyta – Mosses • Sexual reproduction cont’d.:

26. Human and Ecological Relevance of Bryophytes • Pioneer species on bare rock after volcanic eruptions or other geological upheavals = succession • Accumulate mineral and organic matter utilized by other organisms • Retain moisture, and reduce flooding and erosion • Indicators of surface H2O

27. Human and Ecological Relevance of Bryophytes • Peat mosses most important bryophyte to humans • Soil conditioner due to high absorptive capacity • Poultice material due to antiseptic properties and absorbency • Fuel

28. Review • Introduction • Introduction to the Bryophytes • Phylum Hepaticophyta – Liverworts • Phylum Anthocerophyta – Hornworts • Phylum Bryophyta – Mosses • Human and Ecological Relevance of Bryophytes